This proposal has two primary objectives: 1) The large scale production of erythropoietin by kidney cells in culture, and 2) The study of mechanisms regulating formation and secretion of the hormone. Some existing evidence indicates that small, but significant, amounts of erythropoietin can be formed by kidney cells in primary cultures. We are studying the conditions required for maximal formation of the hormone. Cells are subjected to lowered oxygen tension, cobaltous salts, anabolic steroids, and cAMP. We are, in addition, planning to fractionate kidney cells derived by proteolysis, in order to purify those cells responsible for erythropoietin formation.